Circuit arrangement for amplifying electric oscillations



March 22, 1938. M J O, R T 2,111,792

CIRCUIT ARRANGEMENT FOR AMPLIFYING ELECTRIC OSCILLATIONS Filed July 15, 1936 v INVENTOR M-J- 0- STRUTT ATTORN EY Patented Mar. 22, 1938 liiE' CIRCUIT ARRANGEIVIENT FOR ANIPLIIFYING ELECTRIC OSCILLATIONS Maximiliaan Julius Otto Strutt,

Eindhoven,

7 Application July 15,1936, Serial No. 90,790

In the Netherlands July 26, 1935 1 Claim.

As is well known, there is in amplifying circuits comprising amplifying valves retroaction of the anode circuit on the control grid circuit which under certain conditions results in self oscillation 5 of the circuit. In the case of comparatively low frequency of the oscillations to be amplified retroaction is brought about solely by the anodegrid capacity of the amplifying valve. In the case of very high frequencies the retroaction of the anode circuit on the control grid circuit is not only due to the anode-control grid capacity but also to the mutual induction between the cathode lead and the conductors to the auxiliary grids and to the anode. The total reaction in the case of very high frequencies can, however, be reduced to an equivalent impedance between the anode and the control grid which consequently comprises all of the reactions due to the above-mentioned causes. Now, measuring operations carried out on a great number of amplifying valves revealed that this equivalent impedance can be represented by a capacity Cag as is indicated by the formula:

r In this formula Cago designates the static capacity between the anode and the control grid,

f designates the frequency of the oscillations to be amplified and A is a constant which is determined by the mutual induction between the supply conductors.

The formula shows that the equivalent capacity is composed of a positive constant part and a negative part depending on the frequency. Thus, according to the invention'the constant'part of the equivalent capacity or that part which depends on the frequency is so adjusted that for 40 the frequency of the oscillations to be amplified the equivalent capacity is substantially zero.

The constant part Cago of the equivalent capacity may be controlled for example by a suitable choice of the screening between the control grid and the anode within the amplifying valve. The part that depends on the frequency can be controlled by modifying the coupling between the supply conductors to the electrodes of the valve.

The single figure of the drawing shows schematically a tube arrangement used to explain in more detail the various features of the present invention. In said drawing a tube T is shown provided with an anode, a cathode and a control electrode. The control electrode is connected to the cathode of the tube through an external circuit including the grid impedance Zg and the anode of the tube is shown connected to the cathode thereof through the plate impedance Zp. 15 The mutual between the supply conductors is indicated by M and the capacity existing between the grid and plate is indicated by the label Cago. In accordance with the invention, it is evident that the mutual M may be made so as to be equivalent to the capacity between the grid 20 and plate so as to produce an equivalent capacity which is substantially zero for any particular frequency which it is desired to amplify.

The circuit arrangement according to the invention is particularly important in connection with amplifiers that are always tuned to one and the same frequency, as is the case, for example, in television receiving sets. In the case of tunable amplifiers the frequency at which the equivalent capacity is zero may be chosen so as to be equal to the frequency at which self-oscillation would be set up but for the use of the invention.

I claim:

The method of eliminating at a predetermined desired frequency the coupling between the input and output circuits that occurs within the tube structure itself which comprises proportioning the grid-plate capacity of the tube and the mutual inductance between grid and plate leads 0 within the tube to produce equal and opposite a coupling effects at said frequency.

MAXIMILIAAN JULIUS OTTO STRUTT. 

